Current research on soy and breast cancer suggests that moderate levels of soy are safe for survivors, allaying early concerns from animal studies that certain compounds in soy may stimulate the growth of breast cancer cells.

A recently published study claims that soy foods (soy milk, tofu and edamame) and cruciferous vegetables (cabbages, kale, collard greens, bok choy, brussel sprouts, and broccoli) may reduce some common side effects of breast cancer treatment.

The study recruited breast cancer survivors, who were diagnosed between 2006 and 2012, from two ethnic groups: Chinese American (192), including US-born Chinese and Chinese immigrants, and non-Hispanic Whites (173). Researchers focussed on associations between eating soy foods and cruciferous vegetables and menopausal symptoms, joint problems, fatigue, hair thinning/loss, and memory problems.

The study authors reported that women with a higher intake of cruciferous vegetables had fewer menopausal symptoms and less fatigue. When analyses were restricted to each ethnic group, the effect of soy intake was significant only in the non-Hispanic White women, of whom only 20 percent consumed more than 24 g/day of soy products. In Chinese-American patients among whom typical soy food intakes were higher (49 percent exceeded 24 g/day), soy intake was not associated with reduced frequency of symptoms.

Breast cancer survivors are known to experience side effects from cancer treatments that can persist for months or years after the completion of treatment. These problems stem from the fact that many treatments that are designed to prevent breast cancer recurrence suppress the production of estrogen or the use of estrogen by the body.

"These symptoms can adversely impact survivors' quality of life and can lead them to stopping ongoing treatments,” says lead author of the study, Sarah Oppeneer Nomura of Georgetown Lombardi Comprehensive Cancer Center, Georgetown University, explaining the rationale for the study.

However, the current study is based on a cohort of very early stage breast cancer patients, may (>40 percent) of whom did not receive any form of treatment. The alleviation of treatment-related symptoms can only be examined in those patients who received those treatments.

The AICR/WCRF CUP report on breast cancer survivors published in 2014 found indications of links between better survival after breast cancer and soy food consumption. However, the report cautioned that further research is needed. This current study provides some additional insights but is a relatively small study in selected populations and, since analyses were not stratified by treatment status, the impact of these foods on treatment-related symptoms is unclear. It is recommended that patients seek advice from their medical practitioners before making substantial changes to their diet.

The American Institute for Cancer Research is a nonprofit charity designated as tax-exempt under Section 501(c)3 by the Internal Revenue Service. Donations are tax-deductible to the full extent of the law. EIN 52-1238026.